It is known to manufacture such an object by means of an apparatus similar to that described as follows: a circular platform, rotatable about its central axis, hereinafter termed carousel, supports several cylindrical pots also capable of rotation about their vertical axes. The rotation of the carousel brings each pot successively into different positions which correspond to one phase of the manufacturing process. For example, silica-rich pulverulent material is fed into the pot; fusion of said material; cooling of the object produced by fusion; extraction of the object.
The pots, generally of metal, are filled with a refractory pulverulent material which provides thermal insulation. With the pot in rotation, the material is hollowed out in such a manner as to define a cylindrical cavity, the axis of which coincides with the axis of the pot. The bottom and the wall of said cavity have a uniform surface at the end of a reaming operation carried out by moving a blade or cutter vertically and horizontally. Under the action of the centrifugal force, the remaining material remains pressed against the wall of the pot.
The pot, while still rotating, arrives vertically beneath an apparatus for ensuring fusion of the wall and bottom of the cavity thus formed to a certain depth. The apparatus used is generally an electric arc. The material thus melted is a material rich in silica, which may be composed simply of the material serving as insulation, for example sand. But it may be composed of a purer material, for example quartz powder. The latter is deposited in a known manner onto the bottom and the wall of the cavity formed in the insulating material.
When fusion is completed, the carousel brings the pot into another position, where the object produced cools down. From the start of the cooling phase, the motor causing rotation of said pot is stopped.
Finally, the rotation of the carousel brings the stopped pot into another position for the extraction operation. As soon as the object has been extracted from the stationary pot, the material, which is no longer held in place by centrifugal force, collapses. To enable the pot to be used again, it is therefore necessary to reconstruct the central cavity. This return to the initial conditions is bought at the expense of a loss of time and material. Furthermore, the means used for the extraction of the object may cause defects in its surface and may result in it being rejected.